For instance, the year the CN Tower opened was the same year Toronto finally eclipsed Montreal to become the largest and most economically powerful city in Canada.

For Toronto to get there, however, it needed confidence; it needed places that felt new, different and worldly. Up until the 1930s, Toronto had maintained the stiff upper lip of its English and Scottish heritage: a nice place to live and work, but there was little play. Dinner was to be served at home and Sunday was legislated as the Day of Rest.

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And then Toronto got what it needed when a little bohemian community blew a big raspberry at that stiff upper lip. Starting as early as the 1930s but intensifying in the late-1940s, as new arrivals from Eastern Europe blew into town, a Greenwich Village-type scene of artists, coffee houses and art galleries blossomed on Gerrard Street West between Yonge and Elizabeth Streets.

A photo from the September, 1969, issue of Progressive Architecture magazine looks north up Avenue Road past York Square.

Progressive Architecture

However, as development pressure pushed this scene out by the early sixties, a new Bohemia had to be established, and that's when Toronto got what it needed for the psychedelic sixties: Yorkville Village. After establishing itself as the epicentre of the folk movement with the first coffee houses opening in late 1960 and 1961 (and the legendary Riverboat in 1964), Yorkville would become Toronto's Haight-Ashbury from the mid-1960s until the mid-70s. And, because it had indeed started life as a Victorian-era village until it was annexed by Toronto in 1883, it retained the pokiness, charm and the scale of one.

When inevitable development pressure came by the late 1960s, however, Yorkville's hirsute denizens wouldn't stand for glassy towers. And, luckily, neither would "with it" developer Ian (Dick) Wookey, who, in 1968, hired architects Jack Diamond and Barton Myers, both graduates of the University of Pennsylvannia – where they'd studied under Louis Kahn and Robert Venturi – to create York Square at the northeastern corner of Yorkville Avenue and Avenue Road.

"In terms of Canada's planning history, it's just such an important place," said Linda Lewis, Yorkville resident since 1969 and professor emeritus at Ryerson University's faculty of communication and design. "It created the new Yorkville … this integration of old with new, respect for scale and materials, creating a highly dense space in a very small area, which has become characteristic of the rest of Yorkville."

The circular cut-outs in York Square’s brick wall evoked Louis Kahn’s work in India.

Dave LeBlanc/The Globe and Mail

Indeed: Diamond and Myers took a handful of Victorian homes (that had already been turned into shops) and stitched them together via a ground-floor, brick screen sporting massive circular cutouts that recalled Mr. Kahn's work in India. Then, in order to enclose the new complex and create a courtyard, they added low-rise, red brick, angular architecture that didn't steal the show. Accessed by inviting and narrow laneways, the interior courtyard greeted urban explorers with a glorious mess of fire escapes clinging to the rear ends of old houses, more walls with enormous circles, second-storey patios, a large maple tree and various staircases to get around. It's no wonder the first Vidal Sassoon salon in Canada set up here.

It was so groundbreaking, it was splashed across 10 pages of the September, 1969, issue of Progressive Architecture magazine. Billed an "urban supertoy" by senior editor C. Ray Smith, it proved that bulldozing the features that make an area interesting in the first place is counterproductive. The old buildings, he wrote, were retained "specifically so as not to disturb the established flow of already interested people to the location.

"In fact," Mr. Smith continued, "York Square now increasingly attracts a true urban mix of Toronto's population to its shops, activities and restaurants: the young and the old, the curious and the dedicated, the window-shopper and the spender, the square and the hip." Accompanying photographs of dancers, diners, walkers, sketchers and shoppers showed the place buzzing with energy; interior shots of Diamond and Myers's interiors for both Sassoon and woman's retailer Poupee Rouge Boutique showed curved walls and circular cutouts that dialogued with the exterior forms.

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On both the Avenue Road and Yorkville façades, Barrie Briscoe's supergraphics mural in white, green and ochre repeated the circular motif as well as playfully added York Square's very own site plan into the mix. All of these bold moves, Mr. Smith wrote, related to the "megascale of the new metropolis and the new mobile scale of the speeding auto."

The circular windows Mr. Kahn used for York Square still appear elsewhere in the neighbourhood.

Dave LeBlanc/The Globe and Mail

Those Kahn-esque circular windows would appear all over Yorkville – some remain on the parking garage just down the street and at Sassoon's new location on Scollard Street – as would the "secret" laneways, half-up/half-down shop fronts and interior courtyards. Pioneered by Diamond and Myers, these pokey spaces allowed people to linger and explore.

But, more and more, developers are stealing those opportunities away.

"People say, 'Oh, Yorkville's been destroyed, it's not the same,'" Ms. Lewis said. "But the thing that's wonderful about it is it [still] attracts huge numbers of people on their feet, just wandering around, and sitting and gabbing."

Empire Communities is looking to build a large condo tower atop York Square.

Dave LeBlanc/The Globe and Mail

Despite some insensitive interventions that added Styrofoam keystones and pediments, York Square was declared a heritage site in 2014 thanks to Ms. Lewis's hard work. Currently, developer Empire Communities is negotiating with the Ontario Municipal Board as to how much of York Square it must keep before it can erect its condo tower on top. One proposal shows a glass box at the corner of Yorkville and Avenue and, inside of it, one lonely brick wall with four circular cutouts: one wing of a psychedelic butterfly pinned under glass.

Should that happen, Toronto won't get what it needs, but rather what it deserves: a city for developers instead of people.

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The Architectural Conservancy of Ontario is hosting "A Toast to York Square" on Tuesday, Sept. 12 from 5:30 to 7:30 p.m. They write: "Celebration, Commemoration, or Wake – it will be a grand party!" Tickets are $35 and available here.